The invention relates to bleeding hydraulic systems.
A typical automotive hydraulic brake system, for example, includes one or more brake lines. Brake fluid contained within these lines transmits hydraulic force from a brake master cylinder to the hydraulic components (e.g., pistons in drum brakes and calipers in disk brakes) of each of the automobile's brakes. In addition, the brake systems of many modern automobiles equipped with anti-lock brakes include anti-lock brake control units, each of which has a pump and a number of passages, solenoids, and valves.
Over time, brake fluid can become contaminated with water or other volatile impurities, which can corrode or otherwise attack components in the brake system. It is thus desirable, and in some cases recommended by vehicle manufacturers, to replace brake fluid periodically.
And when brake components are replaced (and often when they are damaged), air may be inadvertently introduced into the brake system, especially when the part being replaced, such as an anti-lock brake control unit, includes a number of passages and crevices that can trap air and that are difficult or impossible to purge with brake fluid prior to installation. Because it compresses when force is applied to the brake fluid, air trapped in the brake system reduces the force-transmitting effectiveness of the hydraulic brake system, giving the brake pedal a "spongy" feel and reducing the stopping power of the brakes. Thus, after servicing the brake system, it is typically necessary or desirable to "bleed" trapped air out of the brake system.